A photothermal membrane distillation membrane by layer-by-layer assembly of silver intercalated MXene and a preparation method and application thereof

Abstract

This invention discloses a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene, its preparation method, and its application. It belongs to the field of photothermal membrane distillation system application technology. The preparation method includes the following steps: adding silver nitrate solution and water to a single-layer MXene nanosheet dispersion and then ultrasonically mixing; then mixing with a p-PVDF membrane with one hydrophilic side; after in-situ evaporation, obtaining an Ag@MXene-PVDF membrane; coating its surface with a polyvinyl alcohol solution and then drying to obtain an s-Ag@MXene-PVDF membrane, i.e., the photothermal distillation membrane. This invention also discloses the photothermal distillation membrane prepared by the above method and its application in seawater desalination. The photothermal distillation membrane prepared by this invention exhibits excellent photothermal conversion efficiency, high water flux, and long-term stable operation. It provides a new approach for developing multifunctional photothermal distillation membranes and has broad application prospects in the field of seawater desalination.

Description

Technical Field

[0001] This invention belongs to the field of photothermal film distillation system application technology, and particularly relates to a photothermal film distillation membrane assembled by silver intercalation MXene, its preparation method and application. Background Technology

[0002] Existing seawater desalination technologies that extensively utilize seawater include forward osmosis, reverse osmosis, and capacitive deionization. However, these mainstream methods consume significant amounts of electrical or thermal energy and have extremely high requirements for the feed solution. Membrane distillation (MD), with its theoretical salt rejection rate of 100%, low pressure and low temperature, and ability to treat high-salinity wastewater, is a promising technology in the field of seawater desalination. However, high energy consumption and temperature polarization (TP) issues pose significant challenges to the application of MD. Utilizing renewable energy to reduce TP during operation is crucial for improving the efficiency of MD technology. Photothermal membrane distillation (PMD) technology, with the aid of photothermal materials, uses a membrane to absorb visible light and convert it into heat, thereby reducing energy input during the MD process and lowering TP across the membrane, thus significantly improving MD efficiency.

[0003] The main photothermal materials used in PMD technology include plasmonic metal nanomaterials, inorganic semiconductor materials, and carbon-based nanomaterials. Currently, MXene, a two-dimensional material exhibiting high and broad absorption across the entire solar spectrum, nearly 100% internal photothermal conversion efficiency, and excellent thermal conductivity, has attracted significant attention as a photothermal material for PMD technology. Generally, photothermal conversion involves three mechanisms:

[0004] (1) Localized Surface Plasmon Resonance (LSPR): If the photon frequency matches the intrinsic frequency of electrons on the surface of metal NPs, then resonant photons induce charge-coherent oscillations at the metal-dielectric interface. Surface plasmon resonance decay occurs via two competing pathways: one is radiative decay through photon re-emission causing light scattering, and the other is non-radiative decay, in which hot electrons excited from occupied to unoccupied states are converted into thermal energy. The LSPR effect induces the generation of photothermal electrons and facilitates light absorption, especially in the NIR region. The absorbed solar energy is converted into heat and dissipated into the surrounding medium through lattice scattering vibrations, thereby increasing the surrounding temperature.

[0005] (2) Electron-hole generation and relaxation: mainly occur in narrow bandgap semiconductor materials;

[0006] (3) Conjugation or hyperconjugation effect: The photothermal conversion of several carbon nanomaterials with conjugated structures, including CNTs and graphene, as well as some conjugated polymers such as polypyrrole and polydopamine, is this photothermal conversion effect.

[0007] The study of the photothermal conversion mechanism of MXene is still in the research stage. Some conclusions from existing technologies indicate that the LSPR effect is the main mechanism of MXene photothermal conversion. The numerous hydrogen bonds between MXene nanosheets cause them to stack tightly due to van der Waals forces, which significantly affects water replenishment during PMD (Photothermal Deposition and Control) and thus reduces water production efficiency. Therefore, increasing the interlayer spacing of MXene nanosheets is crucial for the application of MXene as a photothermal material in PMD technology.

[0008] Therefore, how to provide a method for applying MXene nanosheets to photothermal film distillation technology is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention proposes a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene, along with its preparation method and application. This photothermal distillation membrane can absorb solar energy and convert it into thermal energy, reducing energy input during membrane distillation and lowering temperature polarization across the membrane.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A method for preparing a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene includes the following steps:

[0012] Silver nitrate solution and water were added to a single-layer MXene nanosheet dispersion and then ultrasonically mixed. The mixture was then mixed with a p-PVDF membrane that was hydrophilic on one side. After in-situ evaporation and deposition, an Ag@MXene-PVDF membrane was obtained. After coating its surface with a polyvinyl alcohol solution and drying, an s-Ag@MXene-PVDF membrane was obtained, which is the photothermal distillation membrane.

[0013] Beneficial Effects: This invention utilizes in-situ reduction of silver nitrate to generate silver-intercalated MXene nanosheets, effectively solving the stacking problem between single-layer MXene nanosheets and enhancing the photothermal effect. Ag NPs themselves are also photothermal materials, exhibiting a synergistic photothermal effect with MXene nanosheets. Through the redox reaction of silver nitrate and MXene nanosheets, silver nanoparticles can be directly deposited onto the surface of MXene nanosheets, where the MXene nanosheets act as both a reducing agent and an attachment point for the silver nanosheets. After in-situ growth on the MXene nanosheets, the silver nanosheets can act as support points to expand the MXene nanosheets, thereby significantly reducing the stacking problem between nanosheets. Furthermore, the polyvinylidene fluoride (PVDF) base film in this invention has high hydrophobicity and low thermal conductivity, playing a role in hydrophobicity and reducing heat loss. The PDA / PEI hydrophilic coating achieves the bonding between the photothermal coating and the base film. The MXene@Ag coating provides the photothermal effect, and the surface polyvinyl alcohol encapsulates the photothermal coating, preventing it from being washed away during the MD process and isolating it from air during storage to avoid oxidation, while also providing anti-contamination properties.

[0014] Preferably, the method for preparing the monolayer MXene nanosheets includes the following steps:

[0015] An appropriate amount of multilayer MXene nanosheets were added to deionized water and sonicated. After centrifugation, the supernatant was collected, frozen, and then freeze-dried to obtain single-layer MXene nanosheets.

[0016] More preferably, the centrifugation process is repeated twice, that is, after centrifuging the ultrasonically treated multilayer MXene nanosheet dispersion, the supernatant is taken and centrifuged again, and the obtained supernatant is then frozen and freeze-dried to obtain single-layer MXene nanosheets.

[0017] Preferably, the multilayer MXene nanosheets are obtained by etching with an HCl / LiF buffer solution;

[0018] The ultrasound treatment lasted for 1 hour, and the concentration of the multilayer MXene nanosheets after ultrasound treatment was 10 mg / mL.

[0019] The centrifugation speed was 4000 rpm and the time was 20 min;

[0020] The freezing temperature is -50℃ and the time is 12 hours; the freeze-drying time is 120 hours.

[0021] Beneficial effects: Under the above conditions, the MXenes prepared by this invention are all in a monolayer state.

[0022] Preferably, the method for preparing the hydrophilic p-PVDF membrane includes the following steps:

[0023] Tris HCl buffer solution, dopamine hydrochloride (PDA), and polyethyleneimine (PEI) were added to water in sequence. After stirring evenly, the resulting mixed solution was used to soak a polyvinylidene fluoride membrane with one side framed by a tetrafluoroethylene frame. Then, it was washed with deionized water and dried to obtain a hydrophilic p-PVDF membrane.

[0024] Beneficial effects: The base membrane modified by PDA / PEI in this invention has good hydrophilicity and can achieve the combination of base membrane and hydrophilic substances.

[0025] Preferably, the pH of the Tris HCl buffer solution is 8.8;

[0026] The ratio of water, Tris HCl buffer solution, dopamine hydrochloride, and polyethyleneimine added is 100 mL: 5 mL: 200 mg: 200 mg.

[0027] Preferably, the stirring rate is 500 rpm;

[0028] Preferably, the soaking time is 4 hours.

[0029] Preferably, the mass ratio of silver nitrate to monolayer MXene nanosheets is 0:100 to 12:100;

[0030] The concentration of the monolayer MXene nanosheet dispersion is 2.5 mg / mL;

[0031] The concentration of the silver nitrate solution is 0.0~0.8 mg / mL;

[0032] After adding deionized water, the concentration of MXene nanosheets was 0.8~2.0 mg / mL;

[0033] The polyvinyl alcohol solution has a mass concentration of 8 wt%, and the specific preparation method includes the following steps:

[0034] Add 8g of polyvinyl alcohol to 92mL of deionized water, heat at 95℃ and reflux for 6 hours to obtain a polyvinyl alcohol solution with a mass concentration of 8 wt%.

[0035] Preferably, the evaporation temperature is 60°C and the time is 15 hours.

[0036] Preferably, the coating method is to use a doctor blade for coating, wherein the spacing between the doctor blades is 100 μm.

[0037] A method for preparing a layer-by-layer photothermal distillation membrane by intercalating silver-based MXenes.

[0038] Application of a photothermal distillation membrane assembled by silver intercalation with MXene in seawater desalination.

[0039] Compared with the prior art, the present invention has the following advantages and technical effects:

[0040] This invention provides a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene. A polyvinylidene fluoride (PVDF) membrane is used as the hydrophobic base layer, modified with PDA / PEI for hydrophilicity, and then silver nanoparticles are intercalated with MXene as the photothermal layer, followed by coating and encapsulation with polyvinyl alcohol. The photothermal distillation membrane prepared using this invention exhibits excellent photothermal conversion efficiency, high water flux, and long-term stable operation, providing a new approach for developing multifunctional photothermal distillation membranes with broad application prospects in the field of seawater desalination. Attached Figure Description

[0041] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0042] Figure 1 This is a flowchart illustrating the preparation process of the membrane used in photothermal film distillation in Embodiment 1 of the present invention;

[0043] Figure 2 This is an electron microscope image of the monolayer MXene nanosheets prepared in Example 1 of this invention;

[0044] Figure 3 This is a surface electron microscope image of the layer-by-layer assembled photothermal distillation film prepared in Example 1 of the present invention;

[0045] Figure 4 This is a comparison of the photothermal properties of different films prepared in Examples 1 and 3 of this invention;

[0046] Figure 5 This is a schematic diagram of the photothermal film distillation process in this invention. Detailed Implementation

[0047] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] All raw materials used in the embodiments of this invention were purchased through commercial channels.

[0050] The molecular weight of the polyethyleneimine in this embodiment of the invention is 600.

[0051] Example 1

[0052] A method for preparing a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene, such as... Figure 1 As shown, it includes the following steps:

[0053] (1) Hydrophilic modification of polyvinylidene fluoride membrane: Add 5 mL of Tris HCl buffer solution (pH=8) to 95 mL of deionized water, stir at 500 rpm for 5 min, then add 200 mg of dopamine hydrochloride (PDA) and continue stirring until homogeneous. Then add 200 mg of polyethyleneimine (PEI) and continue stirring for 5 min to obtain mixed solution A. Take 25 mL of mixed solution A and soak a PTFE frame (46 mm) in it. A polyvinylidene fluoride (PVDF, Millipore, IPVH00010) membrane with an 86mm frame was soaked for 4 hours. The PVDF membrane was then washed with deionized water and dried to obtain a hydrophilic PVDF membrane p-PVDF.

[0054] (2) Take 1g of multilayer MXene nanosheets obtained by HCl / LiF etching, add 100mL of deionized water and sonicate for 1h, then centrifuge at 4000rpm, take the supernatant and centrifuge again at 4000rpm, freeze the obtained supernatant for 12h, and then freeze-dry for 120h to obtain single-layer MXene nanosheets. The electron micrograph is shown below. Figure 2 As shown, the obtained MXene nanosheets are almost entirely monolayers;

[0055] (3) Take 8g of polyvinyl alcohol, place it in a round-bottom flask, add 92mL of deionized water, reflux at 95℃ for 6h, and cool to obtain a polyvinyl alcohol solution;

[0056] (4) Take 50 mg of the monolayer MXene nanosheets obtained in step (2), add 20 mL of deionized water and sonicate for 10 min, then add 10 mL of silver nitrate solution with a concentration of 0.4 mg / mL, and then add 11.7 mL of deionized water to make the concentration of MXene 1.2 mg / mL. Then sonicate for 30 min to obtain mixed solution B. Take 10 mL of the above mixed solution B and add it to the polyvinylidene fluoride membrane with one hydrophilic side obtained in step (1). Evaporate and deposit in situ at 60 °C in a vacuum oven for 15 h to obtain an MXene loading of 3 mg / cm³. 2 Ag@MXene-PVDF membrane;

[0057] (5) Fix the Ag@MXene-PVDF membrane obtained in step (4) onto the glass plate with tape, and then use a 100µm thick scraper to scrape the polyvinyl alcohol solution obtained in step (3) onto the membrane surface. After drying under natural conditions, the s-Ag@MXene-PVDF membrane, i.e., the layer-by-layer photothermal distillation membrane, is obtained.

[0058] The surface electron microscope image of the resulting layer-by-layer assembled photothermal distillation film is shown below. Figure 3 As shown.

[0059] Technical effects:

[0060] Photothermal film distillation test:

[0061] A direct contact photothermal film distillation testing system (such as a water bath, two peristaltic pumps, a solar simulation light source, a membrane cell with a quartz window, an electronic balance, a conductivity meter, and a constant temperature cooling bath) is used. Figure 5 (As shown) The photothermal film distillation performance of the prepared photothermal film was tested. Both the feed solution and permeate were circulated by a peristaltic pump. The feed solution temperature was 30℃, comparable to the summer seawater temperature in Qingdao, and the flow rate was constant at 30 mL / min. The permeate temperature was stabilized at 20℃, and the flow rate was constant at 150 mL / min. The simulated seawater was a 3.5 wt% NaCl solution, and the light intensity was set at 1 kW / m². 2 The test area is 7×3 cm. 2 The membrane pool depth is 2 mm. Changes in the conductivity and permeate flux of the permeate during the reaction process are automatically recorded using a conductivity meter and electronic balance. The membrane surface temperature change is measured using an infrared thermal imager. The permeate flux J is calculated from the weight change of the permeate using formula (I):

[0062] J = Δm / (ΔT × S) (I);

[0063] In the formula: J is the flux (kg m³) -2 h -1 ), Δm is the permeate weight gain (kg), ΔT is the operating time (h), and S is the effective area of ​​the membrane (m²). 2 ).

[0064] The salt rejection ratio R is calculated based on the conductivity of the permeate, using formula (II):

[0065] R=[(C f -C p ) / C f ]×100% (II);

[0066] In the formula: R is the salt rejection rate, C f Feed concentration (g / L), C pThe concentration of the permeate (g / L). The solution concentration can be calculated from the conductivity based on the linear relationship between conductivity and concentration.

[0067] Calculations show that, under simulated sunlight conditions, the photothermal film prepared in this embodiment can reach a maximum surface temperature of 80.17 °C after 15 minutes of illumination, and a permeation flux of 2.62 kg m³ / h after 2 hours of operation. -2 h -1 The salt interception rate is as high as 99.99%.

[0068] Example 2

[0069] A method for preparing a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene differs from Example 1 in that step (4) specifically includes the following steps:

[0070] (4) Take 50 mg of the monolayer MXene nanosheets obtained in step (2), add 20 mL of deionized water and sonicate for 10 min, then add 10 mL of silver nitrate solution with a concentration of 0.4 mg / mL, and then add 1.3 mL of deionized water to make the concentration of MXene 1.6 mg / mL. Then sonicate for 30 min to obtain mixed solution B. Take 10 mL of mixed solution B and add it to the polyvinylidene fluoride membrane with one hydrophilic side obtained in step (1). Evaporate and deposit in situ at 60 °C in a vacuum oven for 15 h to obtain an MXene loading of 4 mg / cm³. 2 Ag@MXene-PVDF membrane.

[0071] All other process steps and parameters are the same as in Example 1.

[0072] The photothermal film distillation test method is the same as in Example 1. Calculations show that the photothermal film prepared in this example, under simulated sunlight conditions, can achieve a permeation flux of 2.45 kg m³ / h after 2 hours of operation. -2 h -1 The salt interception rate is as high as 100%.

[0073] Example 3

[0074] A method for preparing a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene, differing from Example 1 in that silver nitrate solution is not added in step (4), and includes the following steps:

[0075] (4) Take 50 mg of the monolayer MXene nanosheets obtained in step (2), add 20 mL of deionized water and sonicate for 10 min, then add 21.7 mL of deionized water to make the MXene concentration 1.2 mg / mL, and sonicate for 30 min to obtain mixed solution B. Take 10 mL of mixed solution B and add it to the polyvinylidene fluoride membrane with one hydrophilic side obtained in step (1), and evaporate and deposit it in situ at 60 °C in a vacuum oven for 15 h to obtain an MXene loading of 3 mg / cm³. 2 MXene-PVDF membrane.

[0076] (5) Fix the MXene-PVDF membrane obtained in step (4) onto the glass plate with tape, and then use a 100µm thick scraper to scrape the polyvinyl alcohol solution obtained in step (3) onto the membrane surface. After drying under natural conditions, the s-MXene-PVDF membrane, i.e., the layer-by-layer assembled photothermal distillation membrane, is obtained.

[0077] All other process steps and parameters are the same as in Example 1.

[0078] The photothermal film distillation test method is the same as in Example 1. Calculations show that the photothermal film prepared in this example, under simulated sunlight conditions, can reach a maximum surface temperature of 76.31℃, and a permeation flux of 1.18 kg m³ / h after 2 hours of operation. -2 h -1 The salt interception rate is as high as 100%.

[0079] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene, characterized in that, Includes the following steps: Silver nitrate solution and water were added to a single-layer MXene nanosheet dispersion and then ultrasonically mixed. The mixture was then immersed in a p-PVDF membrane with one side being hydrophilic. After in-situ evaporation and deposition, an Ag@MXene-PVDF membrane was obtained. After coating its surface with a polyvinyl alcohol solution and drying it, an s-Ag@MXene-PVDF membrane was obtained, which is the photothermal distillation membrane. The method for preparing the hydrophilic p-PVDF membrane includes the following steps: Tris HCl buffer solution, dopamine hydrochloride and polyethyleneimine were added to water in sequence. After stirring evenly, the resulting mixed solution was used to soak the polyvinylidene fluoride membrane with one side framed by PTFE. Then it was washed with deionized water and dried to obtain a hydrophilic p-PVDF membrane.

2. The method for preparing a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene according to claim 1, characterized in that, The method for preparing the monolayer MXene nanosheets includes the following steps: Multilayer MXene nanosheets were added to deionized water and sonicated. After centrifugation, the supernatant was pre-frozen and then freeze-dried to obtain single-layer MXene nanosheets.

3. The method for preparing a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene according to claim 2, characterized in that, The multilayer MXene nanosheets were obtained by etching with an HCl / LiF buffer solution; The ultrasound treatment lasted for 1 hour, and the concentration of the multilayer MXene nanosheets during the ultrasound treatment was 10 mg / mL. The pre-freezing temperature is -50℃ and the time is 12 hours; the freeze-drying time is 120 hours.

4. The method for preparing a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene according to claim 1, characterized in that, The pH of the Tris HCl buffer solution is 8.8; The ratio of water, Tris HCl buffer solution, dopamine hydrochloride, and polyethyleneimine added is 95 mL: 5 mL: 200 mg: 200 mg.

5. The method for preparing a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene according to claim 1, characterized in that, The mass ratio of silver nitrate to monolayer MXene nanosheets is 0:100 to 12:

100.

6. The method for preparing a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene according to claim 1, characterized in that, The concentration of the monolayer MXene nanosheet dispersion is 2.5 mg / mL; The concentration of the silver nitrate solution is 0.0~0.08 mg / mL; The final mixed solution contained MXene nanosheets at a concentration of 0.8–2.0 mg / mL. The polyvinyl alcohol solution has a mass concentration of 8 wt%.

7. The method for preparing a photothermal distillation membrane assembled layer by layer using silver-intercalated MXene according to claim 1, characterized in that, The evaporation temperature was 60°C and the time was 15 hours.

8. The layer-by-layer assembled photothermal distillation membrane prepared by the method of preparing a layer-by-layer assembled photothermal distillation membrane by silver intercalation MXene as described in any one of claims 1-7.

9. The application of a photothermal distillation membrane assembled layer by layer with silver intercalation MXene as described in claim 8 in seawater desalination.

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